* What subject did you learn at the first class?
Is this sentence correct?
Do we have to use at or in before the first class?
Can we say "What subject did you learn at the first period?"
Rather than "at" or "in," it'd be better if you used the word "during."
The sentence "What subject did you learn at the first class?" is grammatically correct.
When talking about the specific time when an activity or event took place, we generally use "in" before the time period. However, when referring to a specific event or class, we use "at" before the noun.
So, it would be correct to say "What subject did you learn at the first class?" because we are referring to a specific class.
Regarding your question about using "period" instead of "class," it depends on the context and the education system you're referring to. In some countries, "period" is used to denote a particular time slot for a subject, while in others, "class" is more commonly used. So, you can say "What subject did you learn in the first period?" if that is the correct terminology in your educational context.